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Various forms of optical spectroscopy have heretofore been used for measuring the physiologic variable in living tissue (broadly referred to herein as “Physiologic Spectroscopy” (PS)). For example, some types of optical spectroscopy, such as near infrared spectroscopy (NIRS), have been used to quickly detect changes in hemoglobin thereby sensing when blood volume or flow in a particular organ or tissue changes. Also, optical spectroscopy techniques have been used for determining pH, temperature, oxygen tension, oxygen saturation, partial pressure of oxygen, partial pressure of carbon dioxide, hemoglobin concentration, water concentration, hematocrit, glucose concentration or the presence/absence of a biomarker. In some cases, an optical dye, such as indocyanine green (ICG), can be injected and optical spectroscopy can be used to measure changes in ICG concentration at a particular location and for computing blood flow and/or metabolic rates of oxygen consumption based on those measurements.
However, the use of optical spectroscopy at internal locations within a patient's body (e.g., brain tissue including deep brain tissue, internal organs, tumors, etc.) is dependent upon whether the emitter and/or detector components of the optical spectroscopy system can be operatively positioned near enough to the desired internal location to obtain the desired measurements. PS devices positioned on the surface of the skin have only limited use for monitoring tissues located near the body surface. For example, transcutaneous NIRS devices can be used to assess skeletal muscle oxygenation (SmO2) in patients with heart failure by comparing light absorption at 760 nm and 800 nm as indicia of hemoglobin-myoglobin oxygenation. Wilson, J. R. et al.; Noninvasive Detection Of Skeletal Muscle Underperfusion With Near-Infrared Spectroscopy In Patients With Heart Failure; Circulation, 80(6), Pages 1668-74 (1989). Also, hemoglobin oxygen saturation (StO2) in skeletal muscle has been successfully measured in severely injured trauma patients deemed to be at risk of multiple organ failure using a transcutaneous NIR spectroscopy probe positioned on the surface of the skin. McKinley, Bruce A., et al.; Tissue Hemoglobin O2 Saturation during Resuscitation of Traumatic Shock Monitored Using Near Infrared Spectrometry; Journal of Trauma and Acute Care Surgery, Vol. 48, Issue 4, 637-642 (April 2000). However, optical spectroscopic measurements from skeletal muscle located near the skin may not be indicative of metabolic activity or oxygenation of critical internal organs or tissues for various reasons. For example peripheral blood circulation can be dramatically limited by the administration of vasopressors or vasodilators. Frisch, A., et al.; Potential Utility of Near-Infrared Spectroscopy in Out-of-Hospital Cardiac Arrest: An Illustrative Case Series; Prehospital Emergency Care, Vol. 16, No. 4: Pages 564-570 (2012).
Thus, in some situations it may be more desirable to use PS devices which monitor internal organs or tissues rather than superficial skeletal muscle. For example, NIRS devices have sometimes been attached to the surface of a patient's forehead or scalp to monitor cerebrovascular function. Such devices have proven useful in monitoring cerebrovascular functioning in patients during assisted ventilation and during/after cardiopulmonary resuscitation (CPR). See, Frisch, A., et al.; Potential Utility of Near-Infrared Spectroscopy in Out-of-Hospital Cardiac Arrest: An Illustrative Case Series; Prehospital Emergency Care, Vol. 16, No. 4: Pages 564-570 (2012); Booth E. A., et al.; Near-infrared Spectroscopy Monitoring of Cerebral Oxygen During Assisted Ventilation. Surgical Neurology International; No. 2, Page 65 (2011) and Mullner, M., et al., Near Infrared Spectroscopy During And After Cardiac Arrest-Preliminary Results; Clinical Intensive Care, Vol. 6, No. 3, Pages 107-11 (1995). However, the light emitted from PS devices positioned on the surface of the scalp or forehead may be incapable of penetrating to deep brain tissues because before reaching the brain the light emitted from the device must first pass through the patient's skin, skull bone and meningeal tissues.
The prior art has included some PS devices that can be implanted subcutaneously, thereby avoiding light refraction or damping effects of the skin. For example, investigators have reported use of a subcutaneously implanted NIRS device in combination with an Implanted Cardioverter Defibrillator (ICD). In this study, NIRS oximetric measurements were used, in combination with electrical monitoring by the ICD, to distinguish between the onset of a ventricular arrhythmia requiring defibrillation and mere electromagnetic interference or artifacts resulting from erroneous double counting of the electrocardiographic T-wave as an R-wave, ICD lead failure, or other electrocardiographic aberrancies. Bhunia, S. K. et al., Implanted Near-Infrared Spectroscopy For Cardiac Monitoring; Proc. SPIE 7896, Optical Tomography and Spectroscopy of Tissue IX, 789632 (2011). [http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=733147]
Also, the prior art has included a number of NIRS devices that are positionable at various locations on the patient's skin, subcutaneously below the skin or within certain anatomical passageways or lumens, to measure physiological properties or concentrations of analytes (e.g., pH, temperature, oxygen tension, oxygen saturation, partial pressure of oxygen, partial pressure of carbon dioxide, hemoglobin concentration, water concentration, hematocrit, glucose concentration, presence of biomarkers, etc.) in underlying organs or tissues. Some but not necessarily all examples of such devices are described in U.S. Pat. No. 5,931,779 (Arakaki, et al.); U.S. Pat. No. 6,212,424 (Robinson); U.S. Pat. No. 6,990,364 (Ruchti et al.); U.S. Pat. No. 7,245,373 (Soller, et al.); U.S. Pat. No. 7,613,489 (Myers); U.S. Pat. No. 7,647,092 (Motz et al.); U.S. Pat. No. 8,277,385 (Berka et al.); U.S. Pat. No. 8,346,329 (Xu et al.); U.S. Pat. No. 8,406,838 (Kato) and U.S. Pat. No. 8,649,849 (Liu et al.) as well as United States Patent Application Publication Nos. 2014/0135647 (Wolf II); 2014/0024904 (Takinami); 2013/0225955 (Schenkman, et al.) and 2011/0184683 (Soller et al.) as well as in U.S. Provisional Patent Application No. 62/072,096 entitled Transesophageal Or Transtracheal Cardiac Monitoring By Optical Spectroscopy filed Oct. 29, 2014, the entire disclosure of each such patent and patent application being expressly incorporated herein by reference. Also, examples of such devices are currently marketed as CareGuide™ Oximeters (Reflectance Medical, Inc., Westborough, Mass.); INVOS™ Somatic/Cerebral Oximetry Monitors (Covidien Respiratory and Monitoring Solutions, Boulder, Colo.); Reveal LINQ™ Insertable Cardiac Monitoring Systems (Medtronic Corporation, Minneapolis, Minn.); FORE-SIGHT ELITE® Cerebral Oxygen Monitors (CAS Medical Systems, Inc., Branford, Conn.) and EQUANOX™ Cerebral/Somatic Tissue Oximetry Devices (Nonin Medical, Inc., Plymouth, Minn.). Some if not all of these NIRS devices utilize specialized apparatus and/or signal processing techniques (e.g, “background subtraction”) to minimize or eliminate spectral effects from skin, bone or other intervening tissue that resides between the location of the NIRS device and the organ or tissue of interest.
PS measurements from critical organ tissues (e.g., brain, heart, etc.) could be of greater value than peripheral measurements in many clinical situations, including resuscitation and acute care settings. However, as noted above, transcutaneous devices positioned on the surface of the skin may not be useable to accurately measure physiological variables from certain internal locations because of limitations on the depth of penetration of the light and the need for complex signal processing to subtract or negate the optical effects of whatever light absorbing or refractive matter is located between the light emitter and the target location (referred to generally herein as “intervening matter”). Depending on where the internal location of interest is, such intervening matter may include, for example, skin, fascia, nerves, vessels, muscles, cartilage, bones, connective tissue and body fluids.
Also, PS devices affixed to the surface of a patient's skin may have little or no capability for movement or scanning of tissue. It is desirable for PS devices to be capable of operating at varied wavelengths and/or scanning multiple locations or areas of tissue as such capabilities could be useable for measuring metabolic activity throughout the parenchyma of a particular organ and/or for functional mapping of organs or tissues of interest.
There exists a need in the art for the development of new PS devices and methods capable of overcoming some or all of the above-described shortcomings.